为什么在windows下鼠标点击窗口还是不活动

Question

为什么鼠标点击窗口还是不能激活？ 以下是一个最小的可重现示例：

#include <Windows.h>
#include <strsafe.h>

const int width = 800;
const int height = 600;
LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_MOUSEMOVE:
    {
        const POINTS pt = MAKEPOINTS(lParam);
        // in client region -> log move, and log enter + capture mouse (if not previously in window)
        if (pt.x >= 0 && pt.x < width && pt.y >= 0 && pt.y < height)
        {
            SetCapture(hWnd);
            TCHAR buffer[256];
            StringCchPrintf(buffer, 256, TEXT("xPos: %d, yPos: %d"), pt.x, pt.y);
            SetWindowText(hWnd, buffer);
        }
        // not in client -> log move / maintain capture if button down
        else
        {
            ReleaseCapture();
            SetWindowText(hWnd, TEXT("OnMouseLeave"));
        }
        break;
    }
    case WM_LBUTTONDOWN:
    {
        SetWindowText(hWnd, TEXT("WM_LBUTTONDOWN"));
        break;
    }
    case WM_RBUTTONDOWN:
    {
        SetWindowText(hWnd, TEXT("WM_RBUTTONDOWN"));
        break;
    }
    case WM_LBUTTONUP:
    {
        SetWindowText(hWnd, TEXT("WM_LBUTTONUP"));
        break;
    }
    case WM_RBUTTONUP:
    {
        SetWindowText(hWnd, TEXT("WM_RBUTTONUP"));
        break;
    }
    case WM_CLOSE:
    {
        DestroyWindow(hWnd);
    }
    break;
    case WM_DESTROY:
    {
        PostQuitMessage(0);
    }
    break;
    default:
    {
    }
    }
    return DefWindowProc(hWnd, uMsg, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASS wc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hInstance = hInstance;
    wc.lpfnWndProc = WindowProc;
    wc.lpszClassName = TEXT("main");
    wc.lpszMenuName = NULL;
    wc.style = CS_HREDRAW | CS_VREDRAW;

    RegisterClass(&wc);

    RECT wr;
    wr.left = 100;
    wr.right = width + wr.left;
    wr.top = 100;
    wr.bottom = height + wr.top;
    if (AdjustWindowRect(&wr, WS_CAPTION | WS_MINIMIZEBOX | WS_SYSMENU, FALSE) == 0)
    {
        MessageBox(NULL, TEXT("Error"), TEXT("Error"), MB_OK);
    }
    HWND hWnd = CreateWindow(wc.lpszClassName, TEXT("Windows"), WS_OVERLAPPEDWINDOW,
                             CW_USEDEFAULT,
                             CW_USEDEFAULT,
                             wr.right - wr.left, wr.bottom - wr.top,
                             NULL, NULL, hInstance, NULL);
    if (hWnd == NULL)
    {
        return 0;
    }
    ShowWindow(hWnd, SW_SHOWNORMAL);
    UpdateWindow(hWnd);

    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return 0;
}

我运行程序时，窗口可以正常运行。当我单击另一个窗口时，主窗口变为非活动状态。当我再次点击主窗口时，主窗口无法激活。为什么？

我尝试评论 SetCapture(hWnd) 函数，效果很好。

if (pt.x >= 0 && pt.x < width && pt.y >= 0 && pt.y < height)
{
    //SetCapture(hWnd);
    TCHAR buffer[256];
    StringCchPrintf(buffer, 256, TEXT("xPos: %d, yPos: %d"), pt.x, pt.y);
    SetWindowText(hWnd, buffer);
}